1. Field of the Invention
The present invention relates to an inverter circuit for driving a lamp and a backlight module using the same, and more particularly, relates to an inverter circuit utilizing current control mode to drive the lamp.
2. Description of Related Art
With great advance in the techniques of electro-optical and semiconductor devices, flat panel displays, such as liquid crystal displays (LCD), have enjoyed burgeoning development and flourished in recent year. Due to the numerous advantages of the LCD, such as low power consumption, free of radiation, and high space utilization, the LCD has become the main stream in the market. An LCD includes a liquid crystal display panel and a backlight module. The liquid crystal display panel has no capacity of emitting light by itself so that the backlight module is arranged below the liquid crystal display panel to provide the surface light source for the liquid crystal display panel so as to perform the display function.
Generally, a cold cathode fluorescent lamp (CCFL) is often used in the backlight module for providing a backlight. An inverter circuit is needed to generate a driving signal with alternating current (AC) to drive the CCFL. FIG. 1 is a diagram of a conventional inverter circuit. Referring to FIG. 1, the inverter circuit 100 includes a direct current (DC) voltage source 110, a pulse width modulator 120, a bridge DC/AC converter 130, a transformer 140, and a voltage detector 150. The bridge DC/AC converter 130 is a full bridge DC/AC converter and includes the switches S1 through S4, wherein the switches S1 through S4 are implemented by transistors. Herein, the switches S1 and S4 are classified into a set and the switches S2 and S3 are classified into another set. The two sets of switch are alternately conducted according to the control signals CON1 through CON4 generated by the pulse width modulator 120 for converting the DC voltage provided by the DC voltage source 110 into an AC square wave signal with a high frequency.
The transformer 140 and the capacitors C1 and C2 converts the said square wave signal into a quasi-sine wave signal to drive the CCFL 160. Since the luminance of the CCFL 160 is determined according to the amount of current flowing through the CCFL 160, the voltage detector 150 detects a current flowing through the CCFL 160 and converts the current signal into a voltage signal as a feedback signal fb. Hence, the pulse width modulator 120 adjusts the pulse widths of the control signals CON1 through CON4 according to the feedback signal fb for a purpose of steadily adjusting the luminance of the CCFL 160.
Nevertheless, the bridge DC/AC converter 130 of the said inverter circuit 100 uses too many electrical components, e.g. switches S1 through S4, and the incorrect operation of the switches S1 through S4 may cause the inverter circuit 100 failing to drive the CCFL 160. For example, the switches S1 and S2 are conducted simultaneously. Besides, the conventional inverter circuit 100 often utilizes voltage control mode to drive the CCFL 160. The feedback signal fb generated by the voltage detector 150 is utilized to adjust the control signals CON1 through CON4. However, the pulse width modulator 120 can not immediately adjust the pulse widths of the control signals CON1 through CON4 by utilizing such outer loop feedback path. Hence, the factories and stores are giving many efforts to solve the above-mentioned problems.